While Kutcher and Kunis won't be able to legally tie the knot even if they wanted to, they can still play house. Kunis' own pad is being remodeled, so she's been having slumber parties with Kutcher at his bachelor pad ... and may well stay there.

A source told Us Weekly, "Ashton's male roommate is moving out to make room for her."

"They were friends first, and then it switched to love," the source added. "That's a great foundation for a relationship."

Another friend of the couple added, "They really are perfect for each other."